Novel multidentate pyridyl/thiazolyl ligands containing terpyridine units: formation of dinuclear and trinuclear double helicate complexes.

Abstract

Three new multidentate N-donor ligands L 1–L 3, which contain a combination of pyridyl and thiazolyl donor units, have been prepared starting from 2,2′:6′,2″-terpyridine. The extended linear sequence of ortho-linked N-donor heterocycles (five for L 1; six for L 2; and seven for L 3) is reminiscent of the well-known oligopyridines, although they have different coordination properties due to the presence of five-membered thiazolyl rings which result in natural breaks of the ligand backbone into distinct bidentate or terdentate domains. Thus, the pentadentate ligand L 1 partitions into terdentate and bidentate domains to give a dinuclear double helicate [M 2(L 1) 2] 4+ with Cu(II). The hexadentate ligand L 2 partitions into two terdentate domains to give dinuclear double helicates [M 2(L 2) 2] 4+ with six-coordinate first-row transition metals dications (M=Ni and Co). The heptadentate ligand L 3 partitions into two terminal bidentate and a central terdentate domains to give a trinuclear double helicate [Cd 3(L 3) 2] 6+ with Cd(II). The formation of these complexes highlights the fact that the thiazole group is instrumental in instructing the partitioning of the ligand, which in turn controls the formation of the helicate complexes.